Ovarian Cancer Blood Test - ca 125 used for ovarian cancer detection

The usual ovarian cancer blood test is a check on the level of ca 125 in the blood stream.

It is an important test to have carried out, but not a perfect one. I will explain why.

What is ca 125?

Ca 125 stands for cancer antigen 125. It is a protein that is found in most ovarian cancer cells at a higher level than in normal cells.

This protein is released into the blood stream so a blood test can be used to detect and measure the levels of ca-125.

When measuring the amount of ca 125 in the blood the general view is that more than 35 U/ml is an 'elevated reading'. In general discussion you will hear people just quite the number without the units.

Why isn't it a perfect test?

Simply because too many things aside from ovarian cancer can cause higher than normal levels of ca-125. On top of that some women can have ovarian cancer and still not present a high ca-125 level when this ovarian cancer blood test is carried out.

False positives are perhaps the biggest problem: high readings can be caused by other factors such as endometriosis, benign ovarian cysts, first trimester pregnancy and pelvic inflammatory disease. Particularly pre-menopause the natural cycle makes it much less certain as a predictor.

So how do you interpret the results?

Different medical sources come up with a range of statistics and opinions as to how the readings should be interpreted:

  • It is certainly not clear cut, depending on the stage your cancer has reached you may get the following results^1:
    • with stage I (ie early) ovarian cancer only about 50% will give a positive (high) result;
    • in stages II - IV (ie medium to advanced cancer which has spread from the ovaries) about 80% will give a positive result; but
    • about 20% of ovarian cancer patients show no elevated ca 125 at all
  • If you are being investigated for a pelvic mass then a level greater than 65 is associated with malignancy in around 90% of cases. Without a demonstrable mass the link is much weaker.^2
  • Because of all the other conditions causing elevated levels about only 3% of women with elevated levels have ovarian cancer.^2, 3

So on the one hand this ovarian cancer blood test is an important indicator (80% of stage II-IV cancers giving the elevated ca 125 result), but in healthy women, particularly pre-menopause, the vast majority of high readings won't be cancer.

To further indicate the difficulty of interpreting the results here are some comments on real tests^4

  • One lady had ca 125 of 600 which was only due to a urinary tract infection - the ultrasound showed a cyst on one ovary and she was told there wasn't time for a second opinion and a full hysterectomy was the only option!
  • Another symptomless 67 year old, had an original ca125 of 186 with a mass in her abdomen - stage III ovarian cancer - after 5 chemo treatments down to 16.5
  • A lady aged 32 with severe menstrual cramps. A CT scan showed large cyst, but with her ca 125 level only at 24 it was thought to be benign; however the ovary was removed and it was cancerous - stage I.

Closer to home, 'Mum's' ca 125 was 8,000 when she was first diagnosed after a 'routine' check up on her health insurance with stage 3 ovarian cancer aged 76. A real indicator that all was not well!

Can a sequence of tests be more helpful?

If you know you have cancer then a sequence of tests is often used to monitor progress: - a rise indicates progression or reoccurrence of cancer, a decrease indicates you are responding to treatment

For example, with 'Mum' after 3-4 months of chemotherapy (delivered by the doctors) combined with large parts of the B17 Metabolic Therapy regime (advocated by the family) her ca 125 had come back down to just 127. After a hysterectomy, however, her ca-125 count went back up to 10,000!

The UK National Institute for Health and Clinical Excellence now recognises that when women, particularly women over 50, attend their GP with the repeated or persistent symptoms described previously that checking the ca 125 level is an important ovarian cancer blood test to be carried out.

I would suggest that a sequence of tests could be even more useful. Just as the changes when you know you have cancer indicate the trend of your cancer, a series of readings would more quickly show changes, than a one-off test. As with many things, though, the cost of each test (reportedly around £20) when applied on a large scale can become prohibitive.

Is there a conclusion to be drawn from this?

There are e-mail campaigns circulating in the USA (& elsewhere, being the nature of e-mails) for women to be more aware of this ovarian cancer blood test and to insist on it being carried out when concerned. That is logical in my view, as long as you know that the results need a lot of care when being interpreted.

My second conclusion is that a more definite test should be carried out. So Return to Ovarian Cancer Signs and Diagnosis from Ovarian Cancer Blood Test to find out about an alternative and more definitive test.

Return to Ovarian Cancer Survivors from Ovarian Cancer Blood Test